Systematic study of structural, optical and vibrational properties of solid hydrogen and other simple molecular solids at ultrahigh pressures (greater than 100 GPa, or 1 Mbar), in order to investigate their transitions to the metallic state. Diamond- anvil cell techniques, in conjunction with synchrotron x-ray diffraction and optical spectroscopic methods, will be employed. Emphasis will be placed on measurements on solid hydrogen above 200 GPa. In the 50-100 GPa range, single crystal x-ray diffraction experiments on hydrogen isotopes will be carried out to determine the P-V equation of state, and to characterize structural transitions which have been observed optically. Experiments on rare gas solids and other simple molecular solids will be performed in the 100 GPa range, in order to compare their behavior with solid hydrogen and with theoretical predictions. New high resolution x-ray diffraction methods will be used to extend pressure calibration above 200 GPa, and to study the maximum pressure possible with the diamond anvil cell.
